title: Structure of clean and hydrated α-Al2O3 (1102) surfaces: implication on surface charge.
abstract: Periodic DFT calculations coupled to a first-principle thermodynamic approach have allowed us to establish a surface phase diagram for the different terminations of the α-Al(2)O(3) (1102) surface in various temperature and water pressure conditions. Theoretical results are compared with previous experimental data from the literature. Under a wide range of temperature and water pressure (including ambient conditions) the most stable surface (denoted C2_1H(2)O in this work) is terminated with singly coordinated hydroxyls on four-fold coordinated aluminium (Al(4C)-μ(1)-OH) while most existing surface models are only considering six-fold coordinated surface Al atoms as in the bulk structure of alumina. The presence of more acidic Al(4C)-μ(1)-OH sites helps explain the low Point of Zero Charge (PZC) (between 5 and 6) determined from the onset of Mo oxoanions adsorption on (1102) single crystal wafers. It is also postulated that another termination (corresponding to the hydration of the non-polar, stoichiometric surface, stable in dehydrated conditions) may be observed in aqueous solution depending on the surface preparation conditions.
authors.affiliation: UPMC-Université Pierre et Marie Curie (Paris 06), UMR 7197, Laboratoire de Réactivité de Surface, F-75005 Paris, France.
authors.forename: Asma
authors.initials: A
authors.lastname: Tougerti
authors.forename: Christophe
authors.initials: C
authors.lastname: Méthivier
authors.forename: Sylvain
authors.initials: S
authors.lastname: Cristol
authors.forename: Frederik
authors.initials: F
authors.lastname: Tielens
authors.forename: Michel
authors.initials: M
authors.lastname: Che
authors.forename: Xavier
authors.initials: X
authors.lastname: Carrier